This application is the US national phase of PCT application PCT/AT98/00315 filed Dec. 18, 1998 with a claim to the priority of Austrian application A2150/97 filed Dec. 19, 1997.
The invention relates to a joint (knee joint) for limited relative pivoting of two parts, in particular human body parts, where arcuate guides produce a combined pivoting and sliding.
The problem in making various joints, in particular knee joints, is mainly in reproducing the natural movement of the joint, which natural movement is not a simple pivoting but a combined pivoting and sliding.
Austrian 393,620 describes a joint for a knee brace where two arcuate guides formed in a first brace part are engaged by two pins limiting the pivot angle of the two brace parts. The pins or bolts thus form in every position the axis for the arcuate guiding of the other pins. The natural movement of the knee cannot be duplicated by such an arrangement.
U.S. Pat. No. 5,009,223 describes joints for knee braces where in addition to the two arcuate guides there are two further arcuate guides. These two additional guides form a sort of T, with one T-arm carrying a bolt and the other T-arm another bolt of another side rail. Even in this known arrangement it is not possible to guide in a natural movement.
The object of the invention is to produce a joint of the above-mentioned types that produces a combined pivoting and sliding movement and that is usable in particular but not exclusively as a replacement for a human knee joint. It should also be possible to relatively easily replace wear-prone parts and even produce by changing parts a different movement pattern.
This is attained in that a cam body on one of the pivotal parts, e.g. the tibia, preferably has two sides each with two cams that coact with respective arcuate guides that are formed in cups that are connected with the second pivotal part, e.g. the femur.
Such an arrangement produces a combined pivotal and slide movement that be adjusted by changing the shape of the arcuate guides for different requirements. Replacement of the wear parts is also relatively simple.
According to a preferred embodiment of the invention, the cam body has two cylindrical surfaces forming a cam and meeting at a rounded edge and two projections extending perpendicular to the pivot direction and forming second cams and the guides are offset in two steps in the cups. With this it is preferable when the cam body is shaped in section as a triangle with rounded corners.
The projecting second cams are formed on the side of the rounded triangle opposite the point of the two cylindrical surfaces. The connection of one of the pivotal parts is arranged opposite the point of the two cylindrical surfaces.
In order to hold the two cups these are partially surrounded by a holder on which the connection for the other pivotal part is arranged. The cups are fitted to the holder so that they can be switched easily.